In the standard interpretation of quantum mechanics, the quantum state, also called a wavefunction or state vector, is the most complete description that can be given to a physical system. Solutions to Schrodinger's equation describe not only molecular, atomic and subatomic systems, but also macroscopic systems, possibly even the whole universe.

The most general form is the time-dependent Schrodinger equation, which gives a description of a system evolving with time. For systems in a stationary state (i.e., where the Hamiltonian is not explicitly dependent on time), the time-independent Schrodinger equation is sufficient. Approximate solutions to the time-independent Schrodinger equation are commonly used to calculate the energy levels and other properties of atoms and molecules.